1. Field of Invention
The present invention relates to valve stem seal assemblies of the type installed over valve stems reciprocally movable within valve guides of internal combustion engines, and more particularly to seal assembly retainers incorporating specially designed retention fingers for securement of such assemblies to valve guides.
2. Description of the Prior Art
Those skilled in the art will appreciate the manner in which intake and exhaust valves are employed in cylinder heads of internal combustion engines. Such valves, supported for reciprocal motion within valve guides, include integral elongated stems extending away from the engine cylinder heads, the ends of the stems typically interacting with rotating overhead cams for cyclic opening and closure of the valves during the combustion cycle against the force of valve return springs. Obviously, in order to permit unobstructed reciprocal movement of the stem in the guide, some mechanical clearance must exist between the valve guide and the moving stem. A plurality of valve stems thus move reciprocally to and from the cylinder head, each within its individual guide. So-called valve stem seal assemblies are used to seal against leakage of oil through a mechanical clearance path between each annular engine valve guide and its associated valve stem.
As is well known, the intake port of a combustion chamber is opened and closed by the reciprocating motion of at least one intake valve, which in turn is driven by the rotary motion of a cam, the latter being affixed to and thus rotatable with an engine camshaft. The intake valve permits fuel mixed with air to flow into the combustion chamber. In addition, an internal combustion engine has at least one exhaust valve and associated exhaust port for releasing expended combustion gases to the atmosphere. Typically, intake and exhaust valves are of similar construction, and both include stems integrally affixed to the valves.
In a typical engine, the valve stem seal assembly is fitted over or atop each valve guide, wherein each seal assembly includes a retainer frictionally mounted to an associated valve guide. Each valve stem seal assembly normally has two primary parts: 1) an elastomeric oil seal for controlling leakage of oil between the valve stem and guide as noted, and 2) a structural, usually metallic, cylindrical retainer mounted atop of the valve guide to hold the oil seal in place.
The advantages of using aluminum cylinder heads in small engine applications are already well known to those skilled in the art. However, it is also known that aluminum parts expand more rapidly when heated than do associated steel or cast-iron parts. Thus, apertures in cylinder head decks designed to accommodate the installation of steel or cast-iron valve guides, through which valve stem seals reciprocally move, tend to expand more rapidly than the guides when heated, and to contract more rapidly than the guides when cooled. As a result, it has been difficult to effectively secure valve guides, particularly those formed of steel or cast-iron, in apertures of aluminum cylinder head decks during the entire heating and cooling cycles of such engines.
One solution has been to symmetrically position an internally flanged washer over the aperture of an aluminum cylinder head deck. In such case, the washer has a relatively larger outside diameter than the aperture, and a smaller internal diameter than the aperture through which the guide can be frictionally supported for extension into the aperture. Thus, upon heating of the cylinder head deck, the aperture walls will be able to expand away from the guide without risk of the guide falling into the engine. A more ideal solution, however, would be one that is actually incorporated into the valve stem seal assembly.
The valve stem seal retainer of the present invention addresses the noted guide securement issue, and incorporates a mechanical coupling feature to assure positive retention of the valve guide.
The invention is a novel valve stem seal and retainer assembly for use in an internal combustion engine. A plurality of such assemblies is contemplated for use in an engine; each is designed to physically secure an engine valve guide in place in a cylinder head aperture that expands and contracts during engine operating cycles. Each cylindrical valve stem seal assembly includes an elastomer seal body having a radially inwardly depending sealing lip adapted for continuous engagement with an associated reciprocally moveable valve stem. The lip is adapted to engage the stem to minimize escape of oil lubricant from the engine along a path between the valve guide and the reciprocally moving valve stem seal.
In the disclosed embodiment, the valve stem seal assembly includes a retainer formed of an annular metal body adapted to frictionally retain the elastomer seal body at its upper end. The lower end of the retainer contains first and second sets of axially concentric depending resilient fingers. The first set of fingers extend radially inwardly to mechanically engage and support a unique valve guide member within the body of the retainer for suspension of the guide within a valve guide aperture of a cylinder head deck. The second set of fingers extend radially outwardly, and are adapted to structurally support the seal assembly against the cylinder head deck under a valve spring situated directly against the fingers, and effective to trap the second set of fingers between the spring and deck.